Modelling the direct virus exposure risk associated with respiratory events

The outbreak of the COVID-19 pandemic highlighted the importance of accurately modelling the pathogen transmission via droplets and aerosols emitted while speaking, coughing and sneezing. In this work, we present an effective model for assessing the direct contagion risk associated with these pathogen-laden droplets. In particular, using the most recent studies on multi-phase flow physics, we develop an effective yet simple framework capable of predicting the infection risk associated with different respiratory activities in different ambient conditions. We start by describing the math- ematical framework and benchmarking the model predictions against well-assessed literature results. Then, we provide a systematic assessment of the effects of physical distancing and face coverings on the direct infection risk. The present results indicate that the risk of infection is vastly impacted by the ambient conditions and the type of respiratory activity, suggesting the non-existence of a universal safe distance. Meanwhile, wearing face masks provides excellent protection, effectively limiting the transmission of pathogens even at short physical distances, i.e. 1 m

Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows

Breakup of small aggregates in fully developed turbulence is studied by means of direct numerical simulations in a series of typical bounded and unbounded flow configurations, such as a turbulent channel flow, a developing boundary layer and homogeneous isotropic turbulence. The simplest criterion for breakup is adopted, whereas aggregate breakup occurs when the local hydrodynamic stress $\sigma\sim \varepsilon^{1/2}$, with $\varepsilon$ being the energy dissipation at the position of the aggregate, overcomes a given threshold $\sigma_\mathrm{cr}$, which is characteristic for a given type of aggregates. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a universal scaling among the different flows. For high thresholds, the breakup rates show strong differences between the different flow configurations, highlighting the importance of non-universal mean-flow properties. To further assess the effects of flow inhomogeneity and turbulent fluctuations, theresults are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.Comment: 15 pages, 12 figures, Refinded discussion in Section 2.1, results unchange

Head to head comparison of 2D vs real time 3D dipyridamole stress echocardiography

Real-time three-dimensional (RT-3D) echocardiography has entered the clinical practice but true incremental value over standard two-dimensional echocardiography (2D) remains uncertain when applied to stress echo. The aim of the present study is to establish the additional value of RT-3D stress echo over standard 2D stress echocardiography. We evaluated 23 consecutive patients (age = 65 ± 10 years, 16 men) referred for dipyridamole stress echocardiography with Sonos 7500 (Philips Medical Systems, Palo, Alto, CA) equipped with a phased – array 1.6–2.5 MHz probe with second harmonic capability for 2D imaging and a 2–4 MHz matrix-phased array transducer producing 60 × 70 volumetric pyramidal data containing the entire left ventricle for RT-3D imaging. In all patients, images were digitally stored in 2D and 3D for baseline and peak stress with a delay between acquisitions of less than 60 seconds. Wall motion analysis was interpreted on-line for 2D and off-line for RT-3D by joint reading of two expert stress ecocardiographist. Segmental image quality was scored from 1 = excellent to 5 = uninterpretable. Interpretable images were obtained in all patients. Acquisition time for 2D images was 67 ± 21 sec vs 40 ± 22 sec for RT-3D (p = 0.5). Wall motion analysis time was 2.8 ± 0.5 min for 2D and 13 ± 7 min for 3D (p = 0.0001). Segmental image quality score was 1.4 ± 0.5 for 2D and 2.6 ± 0.7 for 3D (p = 0.0001). Positive test results was found in 5/23 patients. 2D and RT-3D were in agreement in 3 out of these 5 positive exams. Overall stress result (positive vs negative) concordance was 91% (Kappa = 0.80) between 2D and RT-3D. During dipyridamole stress echocardiography RT-3D imaging is highly feasible and shows a high concordance rate with standard 2D stress echo. 2D images take longer time to acquire and RT-3D is more time-consuming to analyze. At present, there is no clear clinical advantage justifying routine RT-3D stress echocardiography use

Short-range exposure to airborne virus transmission and current guidelines

After the Spanish flu pandemic, it was apparent that airborne transmission was crucial to spreading virus contagion, and research responded by producing several fundamental works like the experiments of Duguid [J. P. Duguid, J. Hyg. 44, 6 (1946)] and the model of Wells [W. F. Wells, Am. J. Hyg. 20, 611–618 (1934)]. These seminal works have been pillars of past and current guidelines published by health organizations. However, in about one century, understanding of turbulent aerosol transport by jets and plumes has enormously progressed, and it is now time to use this body of developed knowledge. In this work, we use detailed experiments and accurate computationally intensive numerical simulations of droplet-laden turbulent puffs emitted during sneezes in a wide range of environmental conditions. We consider the same emission—number of drops, drop size distribution, and initial velocity—and we change environmental parameters such as temperature and humidity, and we observe strong variation in droplets’ evaporation or condensation in accordance with their local temperature and humidity microenvironment. We assume that 3% of the initial droplet volume is made of nonvolatile matter. Our systematic analysis confirms that droplets’ lifetime is always about one order of magnitude larger compared to previous predictions, in some cases up to 200 times. Finally, we have been able to produce original virus exposure maps, which can be a useful instrument for health scientists and practitioners to calibrate new guidelines to prevent short-range airborne disease transmission

Upscaling of Electrospinning Technology and the Application of Functionalized PVDF-HFP@TiO2 Electrospun Nanofibers for the Rapid Photocatalytic Deactivation of Bacteria on Advanced Face Masks

In recent years, Electrospinning (ES) has been revealed to be a straightforward and innovative approach to manufacture functionalized nanofiber-based membranes with high filtering performance against fine Particulate Matter (PM) and proper bioactive properties. These qualities are useful for tackling current issues from bacterial contamination on Personal Protective Equipment (PPE) surfaces to the reusability of both disposable single-use face masks and respirator filters. Despite the fact that the conventional ES process can be upscaled to promote a high-rate nanofiber production, the number of research works on the design of hybrid materials embedded in electrospun membranes for face mask application is still low and has mainly been carried out at the laboratory scale. In this work, a multi-needle ES was employed in a continuous processing for the manufacturing of both pristine Poly (Vinylidene Fluoride-co-Hexafluoropropylene) (PVDF-HFP) nanofibers and functionalized membrane ones embedded with TiO2 Nanoparticles (NPs) (PVDF-HFP@TiO2). The nanofibers were collected on Polyethylene Terephthalate (PET) nonwoven spunbond fabric and characterized by using Scanning Electron Microscopy and Energy Dispersive X-ray (SEM-EDX), Raman spectroscopy, and Atomic Force Microscopy (AFM) analysis. The photocatalytic study performed on the electrospun membranes proved that the PVDF-HFP@TiO2 nanofibers provide a significant antibacterial activity for both Staphylococcus aureus (~94%) and Pseudomonas aeruginosa (~85%), after only 5 min of exposure to a UV-A light source. In addition, the PVDF-HFP@TiO2 nanofibers exhibit high filtration efficiency against submicron particles (~99%) and a low pressure drop (~3 mbar), in accordance with the standard required for Filtering Face Piece masks (FFPs). Therefore, these results aim to provide a real perspective on producing electrospun polymer-based nanotextiles with self-sterilizing properties for the implementation of advanced face masks on a large scale

Electrospinning technology for scalable manufacturing of polymer-based nanofibers filters with high-performance in submicron particle filtration and bactericidal activity in advanced face mask

In the recent years, Electrospinning (ES) proved to be an easy and advantageous technique to design functionalized nanofibers mats based on natural and synthetic polymers as well as hybrid bioactive nanomaterials, which can be easily implemented for the realization of advanced wearable healthcare devices, scaffold in tissue engineering, energy harvesting system, etc. In particular, the great advantages to obtain nanofibers with tailored diameter sizes and surface characteristic properties, down to the nano scale, has made this methos commercially attractive to produce ecofriendly and more sustainable high filtering devices for facemask application, especially in the last years when the pandemic outbreak of the Coronavirus disease (COVID-19) have brought to a mass consumption of personal protective equipment (PPE) that resulted in a potential source of further contamination from bacteria or virus. The use of modified electrospinning set-up can be an innovative way to manufacture nanofiber-based membrane showing high filtering performance against submicron pollution particles and suitable antibacterial properties for tackling the current issues from bacterial contamination on PPE surfaces to the reusability of both disposable single use facemask and respirator’s filters

Electrospinning technology to upscale the production of low-cost and high-filtering functionalized polymer-based nanofibers providing photocatalytic activity for bacterial inactivation in advanced face mask

The importance to produce polymer-based membranes with suitable self-cleanable properties in preventing high risk of contamination on the fabric for long time usage has been becoming a relevant issues, especially in the last years when the pandemic outbreak of the Coronavirus disease (COVID-19) have brought to a mass consumption of personal protective equipment (PPE), such as face mask/respirators, which resulted in a potential source of further contamination from bacteria or virus. Modified electrospinning set-ups combined with modern textile techniques turned out to be an innovative way to manufacture nanofiber-based membrane showing high filtering performance against submicron pollution particles and suitable bioactive properties for tackling the current issues from bacterial contamination on PPE surfaces to the reusability of both disposable single use facemask and respirator’s filters [1]. With this paper we aim to provide further insight about the development of advanced electrospun nanofibrous photocatalytic membranes for large scale production. Investigation on the effects of processing variables on the fabrication of functionalized electrospun nanofibers embedded with active NPs for the scale-up line have been carried out by using Scanning Electron Microscopy and Energy Dispersive X-ray (SEM-EDX), Atomic Force Microscopy (AFM), and Raman spectroscopy analysis. In addition, photocatalytic disinfection for some bacteria strains, were conducted on the hybrid polymer-based membranes under UV-A light exposition by using the pristine electrospun membranes as control in the colony count method [2]. Finally, to provide a real perspective for the application of nanotextile in the manufacturing of advanced face mask on large-scale, both particle filtration and breathability test were also conducted on the nanofiber mats, in accordance with the standard required for Filtering Face Piece masks (FFP). [1] Cimini A., E. Imperi, A. Picano, M. Rossi. Electrospun nanofibers for medical face mask with protection capabilities against viruses: State of the art and perspective for industrial scale-up. Applied Materials Today, 2023, (32) 101833. [2] Q. Li, Y. Yin, D. Cao, Y. Wang, P. Luan, X. Sun, W. Liang, H. Zhu, Photocatalytic rejuvenation enabled self-sanitizing, reusable, and biodegradable masks against COVID-19, ACS Nano, 2021, 15 (7), 11992–12005